Abstract: Apparatus and method to improve flow of liquid anhydrous ammonia from a portable liquid NH3 tank in cold temperatures includes an air compressor coupled to the vapor port of a portable liquid NH3 tank used to supply liquid anhydrous ammonia to an anhydrous ammonia fertilizer applicator. The air compressor injects compressed air into the tank to maintain head pressure within the tank at between 80 and 150 psi. to facilitate flow of liquid NH3 from the tank to the applicator when atmospheric temperatures are low as well as when the level of liquid NH3 present in the tank declines.